Silicon and other semiconductor materials are used to construct printed circuit board assemblies (PCBAs) for use in the control of electronic circuits and other devices. In a typical PCBA, conductors and circuit components such as capacitors, resistors, diodes, and the like may be surface mounted or etched onto the PCBA. The PCBA supports as well as electrically interconnects the various components and traces using thin sheets of conductive foil interposed between dielectric layers.
PCBAs, being electric circuits, tend to be highly sensitive to the effects of radiation. Therefore, a common board-level design feature is a Faraday cage. Faraday cages are metal enclosures that are typically surface mounted to the PCBA between sensitive circuit components and the source of radiation. Such cages form electromagnetic interference (EMI) shields around the protected components, and operate by reflecting radiation energy and/or dissipating the energy as heat. Faraday cages may be fastened to an outer surface of the PCBA, or may be located within the board, e.g., as a multi-sided shield protecting PCBA components from internally-generated narrowband fields emanating from adjacent PCBA components. However, Faraday shields and other EMI shielding techniques may not be appropriate in certain applications due to their size and weight, as well as the band-limited nature of their shielding-based principle of operation.
Specifically, Faraday cages and other prior art EMI shields can be relatively large and bulky relative to the components that are being protected. As a result, physical EMI shields typically add an undesirable height or Z-dimension that may be less than optimal or even impracticable for certain applications, particularly those encapsulated in a housing having limited internal space. Additionally, incident field energy may be impinged within any cavities that might exist between the EMI shield and the protected components of the PCBA, thereby leading to undesirable cavity effects. For instance, trapped energy within such cavities may resonate and cause cavity energy to grow exponentially, ultimately damaging the PCBA. Thus, Faraday cages may be undesirable in certain sensitive applications.
Electrically-initiated devices (EIDs) are a particular class of sensitive devices that are triggered or activated via an electrical signal, often while being exposed to intense electric fields. An example EID application is that of an incendiary device used to create a flame or intense heat, e.g., in a sonobuoy operation. For instance, the incendiary device could burn through a small line or lanyard that is maintaining a carbon dioxide (CO2)-based activation function in an off state, with severing of the lanyard causing release of stored CO2. The released CO2 rapidly inflates a sonobuoy floatation device, or alternatively deflates such a flotation device so as to scuttle the sonobuoy when sonobuoy operations are complete. Other EID applications may include pace makers and other medical devices which trigger in response to an electrical signal. As a result, there is a need to protect against premature activation of EIDs due to energy from an incident electric field.